Treatment of cracked hydrocarbon distillates



w.v J. RYAN ETAL TREATMENT OF CRACKED HYDROCARBON DISTILLATES' Filed May1s; 1939 April s, 1943.

Patented Apr. 6, 1943 TREATMENT OF CRACKED VIEI'YDROCARBON DISTILLATES lWilliam J. Ryan, Wilmington, and Marcus T. Kendall, Long Beach, Calif.,assigno'rs, by mesne assignments, to The Tex N. Y., a corporation ofApplication May 13, 1939, Serial o. 273,566

as Company, New York, Delaware 2 claims. (cries-32) This inventionrelates to the chemical treatment of hydrocarbon oils and has to doparticularly with the acid treatment and sweeteningof crackedhydrocarbon distillates.

The present application is a continuation-inpart of pending applicationSerial No. 263,944, led March 24, 1939, (now matured into U. S. PatentNo. 2,249,276) which in turn is a continuation of pending applicationSerial No.

148,260, led June 15, 1937.

In our earlier applications we have described a method of treatingcracked hydrocarbon distillates with sulphuric acid of about 55 to 60%concentration, followed by treatment with strong caustic alkali solutionat a temperature of about 150 to 300 F.

The present invention has to do with a modi- Viication of the foregoingmethod of treatment. It contemplates subjecting the crackedhydrocarbondistillate or distillates to fractionation into light and heavyfractions. These fractions are then subjected to separate chemicaltreatment under conditions of temperature and concentration adapted toproduce a final product of desired characteristics.

In the treatment of cracked hydrocarbon distillates it is customary toemploy sulphurio acid of about 66"v Baume gravity and having an acidconcentration of about 93% H2SO4. The acid treated product, afterremoval of the sludge, is

high-boiling polymerization products inthe vpresence ofconcentratedsulphuric acid.v I

A further advantage of the invention, therefore, is to treat the oil toproduce a product of vthe desired characteristics and containingsubstantially no 'high-boiling polymerized products which normallyrequire redistillation' of the treated oil in order to effect theirseparation Yand removal.

Another advantage of the invention is to carry out the acid-treatingoperation in `such a manner that a product is obtained which may bereadily sweetened withoutv resort to the conventional doctor treatment.f f Still another advantageA of thev invention is to provide means ofsweetening in combination with the acid-treating operation whereby aiinished product is produced much more veconomically and of improved`duality.

In accordance with the' method of the present invention a crackedproduct, such as a cracked naphtha distillate from a cracking still,o-ra mixture of cracked products from several stills or other sources ofsupply, is subjected to fractional distillation so as toseparate it intoa lowboiling fraction and a high-boiling fraction. 'Ihe fractionalseparation is regulated so as to form a light fraction susceptible totreatment with weak t acid without electing substantial polymerizationneutralized, rerun to remove high-boiling point polymerized bodiesv andthen the neutralized .product must 'be treated with `doctor solution Y(sodium plumbite) in order to sweeten it.

--The foregoing type of treatment is objectionof non-gum-formingmaterials. This light fraction may, for example, comprise the majorportion 'or more of the original mixture. e

' This light fraction is then' treated with sulable since theconcentrated acid is relatively nonselective and causes considerable'able products. Y

It has the disadvantage Vof producing higherboiling polymerizationproducts which vimpairl loss of- @valuphuric acid'of about 55 to 60%concentration to remove the gum-formingl constituents. After-removal ofthe acid'sludge the treated fraction-is subjected to the actionof'strong caustic' alkali,

preferably v pose of removing sulphur compounds.

the quality of the oil. High-boiling sulphur-con- ,tainingvcompounds mayalso be produced which impair the quality of the oil so that it isobligatory to use the expensive doctor treatment in .order to convertthe sour high-boiling mercap- .tans intosweet disulphides.

As disclosed `in the aforesaid pending applications, the aboveobjections may be overcome and the objects of our invention obtained byusing certain treating reagents of specied strength and operating in aparticular manner.

One advantage of the method of our invention is to selectively removeguru-forming constituents without substantially affecting the otherconstituents of the oil, such as those ,which form atelevate'd't'emperature, for the' purj vIfl desired, this alkali`ti-'eatmentmay precede the acid treatment.

The heavy or high-boiling fraction, which is substantiallynon-susceptible to the 'formation of high-boiling polymerization'products during treatment with concentrated acid, Ais separatelyktreated with concentratedsulphuric acid of about 98% H2SO4, or inexcess ofabout 80% H2SO4,

- ata temperature between -l-75 F. and +60" F.

This acid-treated heavy fraction is then steamstilled and sweetened.

The acid-treated oil can be sweetened either with sodium plumbitesolution or with hot caustic soda solution under pressure, as will bedescribed later. Itis desirable to steam-Still this In this latter case,the composite cracked naphtha.v

product is then subjected to fractionation into light and heavyfractions,with .recycling ofthe heavy fraction to the cracking stills,the light fraction being chemically treated as already described.

On the other hand, the heavy fraction of the naphtha may be subjected toa separate cracking or reforming action, fwhereby the hydrocarbonconstituents `are mademore amenable andasusceptible to treatment withweak acid inthe manner already described. Thus, the naphtha may besubjected to elevated temperatures'of around 750 to 11'00" F. whileunder pressures ranging from about 50 to600 pounds.

The reformed heavy fraction, after fractionation to remove undesirablehigh-boiling constituents, isrtreated `with `acid of around.55 .to 60%concentration at -about '70 F. so as to remove the-gum-formingconstituents without affecting other constituents. The acid sludge isremoved and the acid-treated oil subjectedto the action of -strongalkalisolutions ata temperature in the range of 150 to 350 F.and Whileundera substantial Vsuperatmospheric pressure. This treatment appears toremove Ythe higher-boiling .point sulphur bodies and any gum-forminghydrocarbons that remain, and thereby produces Aa naphtha which is sweetto the doctor test, low in sulphur content and substantially free fromboth potential and inherent r gum.

The reformed and refractionated heavy fraction may -be blended with theaforementioned lightfractionzand both fractions then treatedtogetherwith vthe aforementioned weak acid of about 55 to 60% concentration,followed by strong caustic sweeteningiunder heat and pressure.

In the acid treatment-of Ythe light fraction, or the reformed -heavyfraction, it .is preferable to employ acid having-a concentration ofaround 55 to 60% 'H2504 at ordinary temperatures. Somewhat strongeracid, for. example, vup to 80% `concentration, Amay kbe used by :furtherreducing vthe temperature to say, "75". The stronger'the ;acid,thelowerrthettemperature which must be used in order toavoid affectingadversely Vother constituents of the oil. Likewise, if temperatures ofabove normal room temperature,.for example, up to 100 F., are employed,the acid concentrationshould not exceed about50% H2804.

-It .has been found that sulphuric acid treatment .of crackeddistillates with acid having a concentration vofover v60% at ordinarytemperatures (60 F. to 75 F.) starts polymerization and, even thoughslight, it increases the gum content andnecessitates rerunning to removethis gum of polymerization.

Treatment with kacid of less 4than `55% H2SO4, at about ordinarytemperature, fails to remove a substantial portion of the 4inherent gum(naturally present-in the raw gasoline) andthus the gasoline is'unitforcommercial use.

On the other hand, it has been definitely ascertained that sulphuricacid of a strength between 55% and 60% H2804 has a particularlyselective action on cracked distillates at ordinary temperatures-thatis, around normal room tempera-ture. Such treatment removessubstantially all the unstable gum-forming constituents and at the sametime avoids the polymerization of relatively stable or non-gum-formingconstituents. For example, if the gum formation is due to diolefins, itis desirable to selectively remove these compounds without substantialpolymerization c-f other olefin compounds. It has been found that Yagumstable product may be obtained with- .out measurable.eiect on otherproperties, such as Vanti-knock, color, etc.

The particular manner of applying the `acid may be varied considerably.Good results have been obtained by adding the acid portion-wise. Weprefer to use from 2 to 5 dumps of acid, al-

.thoughn some cases itmay .be satisfactory to use only .one dump.`A'total of about A2te l2 .pounds of .acid .perbarrel of ioil is.ordinarily sufcient. Any well-.known or preferred method of contact maybe used, such as orifice plates or mechanical mixers, although We prefera counterlow type of operation. Ordinary'temperatures may rbe used,Valthough it isV contemplated that low temperature acid treatment maybeemployed.

rIhe acid-treated product, afterseparation of the acid sludge, isneutralized in the Vcustomary 'ma nner with aqueous caustic alkali orvcaustic soda. A caustic sodasolution of v'about 5 degrees Ba um gravityis `ordinarily used. In some cases this preliminary neutralizing stepmay be omitted and the acid-treated product subjected directly to thehot alkali treatment described hereafter;

The aci reated product labove Vdescribed should be substantially freefrom high-boiling polymerized products and as a result the end pointshould not be materially altered, whereby redistillation would berequired. The product is also essentially free from sulphur compoundswhich are refractory and diflicult to treat. -Accordingly, the productso previously treated is peculiarly adapted `for the hot alkalitreatment in place of the more expensive, customary doctor treatmentwith sodium plumbite.

The alkali treating or sweetening step is carried out by contacting theoil by any suitable means with a strong alkali solution such as causticsoda. The strength of alkali may be varied and one skilled in the artwill'be able'to determine the required 4strength `to obtain the desiredresults. I

We have found solutions varying from 20 to50 degrees Baum gravitysatisfactory, and" prefer to use about 45 degrees gravity. Thetemperature of treatment should be at least about degrees F. and may beas high as 300 degrees F. or more. We prefer temperatures around 200 to210 degrees F.

The mixture is also maintained under a substantial superatmosphericpressure. This pressure may be that self-generated by confining thevapors of the mixture and should be at least about 50 pounds, althoughpressures cf 150 or even up to 500 pounds or more are contemplated. Weprefer about 60 to 100 pounds pressure.

It is essential for the success of the sweetening step of the inventionthat substantially no polymerization takes place in the acid-treatingstep. Without restricting the invention in any Way to a'particulartheory of reaction, it is believed that when polymerization occurs,highboiling point rnercaptaris are formed, which will not react with thecaustic soda, even under the influence of heat and pressure, and as aresult, normally would require the use of plumbite to convert them todisulphides. The present invention provides means for selectivelydissolving the inherent gum and substantially preventingpolyrnerization.

'Ihe invention is particularly advantageous for treating highsulphur-content oils, such as obtained from California petroleum. It issimple and eicient and eliminates the expensive doctor treatingoperation and substitutes a simple caustic treatment. The reagents,particularly the caustic solution, may be recovered and restored tosubstantially the original activity by releasing the pressure andsteaming.

Instead of first acid-treating the oil and then subjecting theacid-treated product to the hot alkali treatment, it is sometimesadvantageous to give the oil the hot alkali treatment prior to theacid-treatment. It is contemplated, therefore, that the untreated oilmay be first subjected to treatment with strong alkali substantially asdescribed, the alkali-treated product treated with the sulphuric acidand the acidtreated product neutralized with dilute caustic solution toproduce a finished product. For example, a cracked naphtha was treatedat a temperature of approximately 325 degrees F. and under a pressure ofabout 175 pounds with a caustic soda solution of approximately 25C Baumgravity, whereby the sulphur compounds were substantially removed. Thetreated naphtha was then subjected to the above described weak acidtreatment. The acid-treated product was then neutralized with a weakercaustic soda solution to produce a sweet, gum-stable product of lowsulphur content.

While we have specified caustic soda solution. it is contemplated thatother compounds of the alkali metals or of the alkali earth metals arewithin the scope of the invention.

The present invention has the advantage over the conventional method of.treatment in that the cost of chemicals is materially decreased,treating losses are reduced and the anti-knock value of the nishedproduct is increased. It has been found, for example, that treatingcosts may be reduced 50-75% by our invention; that treating losses maybe as much as 60% lower and that the anti-knockl value of the finishedproduct may be several points higher than normally obtained.

In order to describe the invention further reference will now be made tothe accompanying drawing comprising a flow diagram of the operationsreferred to above.

Feed oil to be cracked or converted into gasoline hydrocarbons isconducted from a source not shown through a pipe I to a heater 2 whereinthe oil is heated to a temperature in the range 750 to 1100 F. Theheated hydrocarbons are passed from the heater .2 through a pipe 3 to acracking stage 4 wherein conversion into gasoline hydrocarbons occurs.

The cracked hydrocarbons are conducted from the cracking stage through apipe 5 to a fractionating stage 6.

In the fractionating stage the naphtha components are separated from theheavier hydrocarbons, which latter are drawn oil as bottoms through apipeyl, The naphtha components are separated into low boiling andhighboiling fractions respectively. The low boiling fraction isconducted through a pipe 8 to an acid treating stage 9, while the highboiling fraction is conducted through a pipe I0 to a receiver or tank lI The low boiling naphtha is subjected to contact in the stage 9 withsulfuric acid containing about 50 to 60% H2804 at a temperature of about60 to '75 F. The resulting sludge is drawn off through a pipe I2 whilethe acid treated naphtha is conducted through a pipe I3 to an alkalitreating stage I4 wherein it is subjected to treatment with concentratedcaustic alkali solution. The alkali treatment is advantageously effectedat a temperature in the range about to 300 F. and under superatmosphericpressure.

'Ihe resulting sludge is discharged through a pipe I5 while the alkalitreated naphtha is discharged through a pipe I6, which may communicatewith a pipe I1 leading to a blending tank I8.

The high boiling naphtha fraction accumulating in the tank II isadvantageously recycled all or in part through a pipe 20 communicatingwith the previously mentioned pipe I.

That portion of the naphtha which is not recycled may be conductedthrough a branch pipe 2l to an acid treating stage 22 wherein it istreated with concentrated sulfuric acid.

The resulting sludge is discharged through a pipe 23, while the treatednaphtha hydrocarbons are conducted through a pipe 24 to a steam stillingstage 25, The steam stilled naphtha is conducted through a pipe 26 to analkali treating stage 2'! wherein neutralization or sweetening iseffected. The sweetened naphtha is discharged through a pipe 28 and mayall or in part be conducted through a branch pipe 29 cornmunicating withthe previously mentioned tank I8 wherein the sweetened naphtha isblended with the previously mentioned light naphtha fraction.

Obviously many modications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof and therefore only such limitations should be imposedas are indicated in the appended claims.

We claim:

l. In the manufacture of gasoline, the steps which comprise subjectinghydrocarbon oil having a high sulphur content to thermal conversion byexposure to elevated temperatures in the range at which higher boilinghydrocarbons undergo conversion into lower boiling hydrocarbons, formingcracked naphtha distillate of high sulphur content containinggum-forming constituents as well as non gum-forming polymerizableconstituents. separating said distillate into a lower boiling fractioncontaining constituents susceptible to formation of high boilingpolymerization products at ordinary temperature when in the presence ofsulfuric acid having a concentration in excess of 60% HzSOi, and ahigher boiling naphtha fraction substantially free from suchconstituents and containing gasoline hydrocarbons in substantial amount,subjecting the lower boiling fraction to the action of sulfuric acid ofabout 50 to 60% HzSOi, and at a temperature of about 60 to 75 F. wherebygum-forming constituents are removed without substantially affectingother constituents, removing the acid sludge, subjecting the acidvtreated oil to the action of concentrated ,caustic perature in thepresence of fresh charge oil and wherein it undergoes furtherconversion.

2. The method according to claim 1 in which the thermal conversion iseffected at a tempera- 5 ture in the range T50 to 1100 F.

WILLIAM J. RYAN. MARCUS T. KENDALL.

CERTIFICATE CE CORRECTION. Patent No. 2,515,758.A AApr-11 6, 1915.

WILLIAM J. RYAN, ET AI..

It is hereby certified that error appeare in the printed specificationof the abovernumbered patent requiring correction'as follows: Page l,second column, line )4.9, fr between +75'o F."read --between T750 F.;and

that the said Letters Patent should be read with this Correction thereinthat the samemay -conform to the record of the Case in the PatentOffice.

signed andsealed this 25th day ofmay, A. D. 19M.

Her-11'5-r Van Arsdale, v (Seal) Acting Cnunissiener of Patents.

